docs(cli): add desktop Steam lifecycle guidance via steamcli client

cli-tooling.md

@@ -51,6 +51,24 @@ Before writing a script to do something, check whether:
 - the tool you are already using has a subcommand for it,
 - the project's own `scripts/` directory already contains it.
 
+### Desktop Steam Client Lifecycle (`steamcli`)
+
+> [!TIP]
+> **Never spawn Steam via raw shell backgrounding (`nohup steam &` or `steam -silent &`) or kill it with `pkill`.**
+> On desktop Linux/Bazzite, raw spawning leaves orphaned bash wrappers, misses custom client flags, or fails to initialize properly.
+> Instead, manage the desktop Steam client through **`steamcli client`**:
+> ```bash
+> # Graceful exit and wait for it to finish flushing configuration:
+> steamcli client shutdown
+>
+> # Launch the desktop client cleanly with configured defaults:
+> steamcli client launch
+>
+> # Launch with custom Steam arguments:
+> steamcli client launch -- -silent
+> ```
+
+
 ---
 
 ## 2. Non-Interactive Invocation